Of all the Koopa shell models I've seen, Conceptify has definitely made the best remix of "Turtle Shell Racer High Power Edition Repaired" by red112, which originally was "Turtle Shell Racer High Power Edition" by Skimbal... But me being me, I wasn't happy with a few things.
I cleaned up the bottom and gave it a flat spot for easier printing.
I made the Top shell and bottom shell each it's own piece, instead of two. (hated the seam)
I hollowed out the bottom shell to use less filament.
I sorta carved out a little on the top of the bottom shell so the top shell would fit in better and hide the seem. I did this part a little lazily, so a bit of sanding will be required, but it's under the shell so it doesn't need to look perfect.
I took off the squared part for the wings to print on. I thought it looked bad and was unnecessary.
Spike is unchanged, but thought I should include it.